Chapter Outline
 8.1 Solutions and Their Concentrations
 8.2 Dilutions
 8.3 Electrolytes and Nonelectrolytes
 8.4 Acids, Bases, and Neutralization Reactions
 8.5 Precipitation Reactions
 8.6 Oxidation-Reduction Reactions
 8.7 Titrations
 8.8 Ion Exchange
(electron transfer reactions)
Section 8.6 - Oxidation-Reduction Reactions
Oxidation-Reduction Reactions (Redox):
Characterized by gain or loss of electrons
by atoms involved in the reaction.
Oxidation:
Table 8.4 - Oxidation Number Rules
The charge the atom would have in a molecule (or an ionic
compound) if electrons were completely transferred, i.e.
applies to both ionic and covalent compouinds.
1. O.N. = 0 for atoms in pure elements.
Historical definition =
Modern definition =
Reduction:
2. O.N = the charge on monovalent ions
Historical definition =
Modern definition =
3. O.N. of fluorine = -1 for all of its compounds
4. O.N. of oxygen = -2 in nearly all of its compounds
5. O.N. of hydrogen = +1 in nearly all of its compounds
6. O.N. values of the atoms in a neutral atom sum to zero
7. O.N. values of the atoms in a polyatomic ion sum up to
the charge on the ion
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Sample Exercise 8.9
What are the oxidation states for sulfur in (a) S8, (b)
SO2, (c) Na2S, and (d) CaSO4 ?
Electron Transfer in Redox Reactions
oxidation
lose n electrons
O.N. = +n
reduction
gain n electrons
O.N. = -n
Sample Exercise 8.10:
Identifying Oxidizing and Reducing Agents and
Determining Number of Electrons Transferred
Energy released by the reaction of hydrazine and
dinitrogen tetroxide:
2 N2H4(l) + N2O4(g) → 3 N2(g) + 4 H2O(g)
Oxidizing Agent =
Reducing Agent =
Is used to orient and maneuver spacecraft and to propel
rockets into space. Identify the elements that are oxidized
and reduced, the oxidizing agent, and the reducing agent,
and determine the number of electrons transferred in the
balanced chemical equation.
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